The present invention is in the field of semiconductor and printed-circuit-board (PCB) manufacturing including surface mount technologies (SMT), and pertains more particularly to methods and apparatus for applying protective coatings to structures meant for connection by BGA and other techniques.
The field of integrated circuit interconnection and packaging is one of the most rapidly-evolving technologies associated with semiconductor manufacturing. As demand for devices that are smaller and more powerful continues to increase, pressures are put on manufacturers to develop better and more efficient ways to assemble and package IC products. One of the more recently developed methods for assembling and packaging IC products is known as Ball-Grid-Array (BGA) technology. Motorola(trademark) inc. is one of the noted pioneers of BGA technology. Currently there are many companies that license BGA technology developed by Motorola(trademark), and Motorola(trademark) and other companies continue to develop BGA technology.
BGA technology provides several advantages over more mainstream technologies such as Fine-Pitch-Technology (FPT), and Pin-Grid-Array (PGA). One obvious advantage is that there are no leads that can be damaged during handling. Another obvious advantage is that the solder balls are typically self-centering on die pads. Still other advantages are smaller size, better thermal and electrical performances, better package yields, and so on.
In BGA technology, wafers or substrates are typically protected with a non-conductive material such as a nitride layer. The die pads are exposed through the nitride layer by means of chemical etching, or by other known methods. The protective nitride layer is intended to protect the substrates from contaminants and damage. One problem with prior-art protective coatings such as a nitride layer is that it is ultra-thin and does not offer any protection to the die pads themselves nor to the connection points between solder balls in the die pads.
It has occurred in the inventor that an additional protective coating, such as a protective polymer-based coating, would offer a measure of protection not provided with prior-art coatings. For example, it is desired that in addition to protecting the substrates itself, die pads and soldered connections may also benefit logically from protection. However, in order to obtain the added, protective benefits from an additional coating, a unique application process must be conceived. It is to such a process that the method and apparatus of the present invention is directed.
In the development of protective coating technology for BGA devices and other contact schemes the inventors have also discovered that a similar technique also provides vastly increased lateral strength for connections made to connection pads on BGA assemblies and other sorts of devices wherein connection extensions to pads are necessary.
Accordingly, what is clearly needed is a method and apparatus for applying a protective overcoat to a devices after adding contact extensions such that exposed die-pad areas, soldered connections, and exposed areas of solder balls in the assembly are protected from exposure, and the contact interfaces are strengthened.
In a preferred embodiment of the present invention a method for providing electrical contact to pads on a surface of a device is provided, comprising the steps of (a) adding a first contact extension to individual ones of the pads; (b) covering the pads and contact extensions with a layer of protective material; (c) removing a portion of the layer of protective material such that a portion of each of the contact extensions is exposed; and (d) applying a second contact extension to individual ones of the exposed first contact extensions.
In a preferred embodiment of the invention the first contact extensions are one of solder or wire extensions. Also, the protective material may be applied by one of screening, spraying, dispense and spinning, or injection into a mold, and removal may be by one of physical machining or etching. In preferred embodiments the second extension is of the same material as the first extension, and a contiguous interface is provided. In some instances the first extension is a solder ball, providing a ball-grid array (BGA), and in some instances the second extension is also a solder ball.
In another aspect of the invention an electrical contact system is provided, comprising a first surface of a device having electrical contact pads; a first contact extension bonded to individual ones of the pads at a first interface; a layer of protective material encapsulating the first interfaces and at least a portion of the first extensions; and a second contact extension bonded to individual ones of the first contact extensions. In some embodiments the first contact extensions are one of solder or wire extensions, and the protective material is a polymer material. Further, the second extension may be of the same material as the first extension, and a contiguous interface is provided.
In some embodiments of the invention the first extension is a solder ball, providing a ball-grid array (BGA), and in some embodiments the second extension may also be a solder ball.
In embodiments of the present invention taught in enabling detail below, for the first time a method and apparatus is provided for protecting and strengthening vulnerable electrical contacts made to contact pads on many electronic devices.